SLITTERS & REWINDERS | MACHINERY
Rolling back: slitting and rewinding
Effective slitting and rewinding ensures that finished product is gathered efficiently – without either delay or damage
Rewinding may seem little more than a formality in the extrusion process, but technical challenges such as film shrinkage – and the sheer weight of the rolls – need to be carefully managed in order to ensure that the product is not damaged. Davis-Standard has developed an ironing roll winder for larger diameter master rolls up to 1.2m (4ft) in diameter on cast film lines up to 6m (20ft) wide. The company says that the technology is most beneficial for CPP and barrier films where post wrap shrinkage occurs as a result of the types of polymers used in the film structures, or where blocking can occur due to a soft sealant layer with a high coefficient of friction (COF). The winder incorporates programmable tension
control, pre-spreading onto the winding roll, and servo-controlled web entry of the film to influence levelling or lay-flat of the film prior to the lay-on roll. Roll hardness is improved with a more precise loading force of the lay-on roll against the winding roll, controlling the in-wound air at higher produc- tion speeds than previously possible. When optimised these features can reduce defects such as tin-canning, caused by blocking and entrapped air, and resulting in annular raised bands on the roll face. Other defects such as buckling, telescoping, and starring can also be reduced with the control features and dynamics of the new winding system. The variable geometry of the ironing roll enables processors to pre-wrap the film onto the winding roll prior to the lay-on roll, allowing entrapped air to reduce the COF between each
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wrap. This promotes film flatness prior to engaging roll hardness with the lay-on roll, says the company – resulting in improved control, preventing in- wound imperfections. The winder is available with a tapeless static knife or patented stationary knife automatic transfer systems, and shafted or shaftless operation to further support efficiency. Although the winder is primarily designed for large master roll winding, in-line slitting is also possible in some shafted applications.
Slitting range At this year’s Chinaplas, Goebel IMS will showcase three of its machines: Monoslit, Interslit and Xtraslit 2. The company’s portfolio covers web widths from 1,800 to 12,000mm. All its slitter rewinders use a digital AC drive technology to reduce operational costs and energy consumption. The technology can recover energy from web tension or during the deceleration at the end of each winding cycle. The Interslit is aimed at manufacturers of special films with a width between 4,000 and 7,000mm. These include biax, battery separator, optical or ultra-thin films as well as transfer printing applica- tions. The slitter rewinder is suitable for foil thick- nesses of 0.5 to 500 microns. Its winding stations can accommodate a roll weight of up to 5,000kg with an unwind diameter of up to 1,550mm and a rewind diameter of up to 1,300mm. Although working with sensitive materials and heavy rolls, it has top speeds of up to 1,200m/min.
Main image: Davis-Stand- ard’s ironing roll winder is aimed at larger diameter master rolls
� April 2018 | FILM & SHEET EXTRUSION 31
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